(a) Field of the Invention
The present invention relates to a polycrystalline silicon formation apparatus, and more particularly to a polycrystalline silicon formation apparatus capable of reducing or eliminating defects and impurities.
(b) Description of the Related Art
Solar cell is a kind of semiconductor, and is also known as solar chip, and silicon is a material generally used for manufacturing solar cells, whose power generation principle is to convert solar energy into electric energy. Solar PV cells are made of various different materials including monocrystalline silicon, polycrystalline (or multicrystalline) silicon, amorphous silicon and other non-silicon materials, wherein monocrystalline silicon and polycrystalline silicon are commonly used, and the monocrystalline silicon is composed of atoms arranged according to a specific rule, and each crystal grain in the region of the polycrystalline silicon has its own arrangement, and the structure of a grain boundary between crystal grains is relatively incomplete and accumulated with impurities easily, and thus resulting in a higher detective rate, and affecting the efficiency of converting solar energy into electric energy by the solar cell. The monocrystalline silicon solar cell provides higher conversion efficiency, but it incurs higher manufacturing costs. Although products available in the market at an early stage are still based on the monocrystalline silicon, polycrystalline silicon tends to take over the position of monocrystalline silicon in recent years, since the monocrystalline silicon has a higher cost, and the development of polycrystalline silicon advances to improve the conversion efficiency of polycrystalline silicon and lower the cost of polycrystalline silicon.
With reference to FIG. 7 for a conventional way of forming crystalline silicon, a crystal growing silicon material 14 is placed into a crucible 11 to form a crystal grain 21 in the crucible 11 under the effect of a unidirectional solidification at a heater 12 installed on both sides of the crucible 11 and an external crucible 13 disposed on the external periphery of the crucible 11, and the crystal grain 21 is solidified in unidirection and grown upwardly to form a complete polycrystalline silicon 2 as shown in FIG. 3, and finally the polycrystalline silicon 2 is diced, ground, polished and sliced into a wafer substrate of a specific size and provided for manufacturing the solar chips.
Each crystal grain of the polycrystalline silicon is isolated by a “grain boundary”, and most grain boundaries of the polycrystalline silicon formed by the aforementioned conventional method are electro-active grain boundaries, and excited electron holes passing through a region of the electro-active grain boundary are captured and cannot be transferred through an electrode or used, and the region of the electro-active grain boundary becomes invalid. If the excited electron holes pass through a region of an electrically inactive grain boundary, the electron holes will not be recombined. Thus, it is very important to control the electro-passive grain boundary or reduce the electro-active grain boundary in the polycrystalline silicon manufacturing technology. The twin boundary is an electrically inactive grain boundary. The more the twin boundaries, the better the quality of the polycrystalline silicon.